Recently, the in vitro fertilization of zona-free hamster eggs was proposed as a test for human sperm fertilizing ability. This test may be a powerful tool in male infertility research. However, the test requires verification because relatively small populations of men were studied and the incubation conditions in the test were not thoroughly examined. Through the collaborative efforts of the Gynecological Infertility Clinic and the Male Fertility Unit of the Johns Hopkins Hospital we propose to critically evaluate the validity of this fertilization test for human sperm fertilizing ability. Childless couples will be evaluated to determine the fertility of each partner. Infertile men will be identified and, together with fertile donors, will be tested with the fertilization assay. In the assay, spermatozoa will be capacitated by incubation in Biggers, Whitten and Whittingham's medium (BWW). The spermatozoa will then be combined with hamster eggs which have been previously treated with hyaluronidase and trypsin to remove cumulus cells and zonae pellucidae, respectively. After two hours the eggs will be fixed, stained, and assessed for fertilization. The results of these studies will be statistically evaluated to determine the sensitivity, specificity and predictive values of the assay. Thus, the validity of the assay can be determined. Since previous studies failed to examine the sperm incubation conditions used in the assay, we propose to study the effects of varying sperm concentration and incubation time in BWW medium on the results of in vitro fertilization tests. Thus, optimal sperm incubation conditions will be determined and the assay can be refined. Finally, we propose to determine if a direct correlation exists between in vitro fertilization test results and human fertility by comparing fertilization test results with pregnancy rates achieved by patients after varicocele repair or vasectomy reversal. If the assay is capable of predicting fertility in these patients, our studies can be expanded to determine the ability of the assay to diagnose the fertility, and to evaluate the medical treatment, of men suffering from other infertility-related disorders.